The present invention relates to construction equipment, such as cranes. In particular, the present invention relates to a crane having a hydraulic circuit to control a hydraulic boom hoist cylinder. Aspects of a crane incorporating the preferred embodiment of the invention are disclosed in the following pending U.S. patent applications: patent application Ser. No. 08/834,673, filed Apr. 1, 1997; patent application Ser. No. 08/834,724 filed Apr. 1, 1997; patent application Ser. No. 60/041,555, filed Apr. 16, 1997; patent application Ser. No. 08/845,843, filed Apr. 25, 1997; patent application Ser. No. 08/826,627, filed Apr. 3, 1997; patent application Ser. No. 08/842,974, filed Apr. 25, 1997; and patent application Ser. No. 08/950,870, filed Oct. 15, 1997; the disclosures of which are hereby incorporated by reference.
Construction equipment, such as cranes or excavators, often must be moved from one job site to another. Moving a crane or, an excavator can be a formidable task when the machine is large and heavy. For example, highway limits on vehicle-axle loads must be observed and overhead obstacles can dictate long, inconvenient routings to the job site.
One solution to improving the mobility of large construction machines, such as cranes, is to disassemble them into smaller, more easily handled components. The separate components can then be transported to the new job site where they are reassembled.
The typical practice has been to use an assist crane to disassemble the crane into the separate components. The assist crane is then used to load the components onto their respective transport trailers. Once at the new job site, another assist crane is used to unload the components and reassemble the crane. As the components for a large crane can weigh as much as 80,000 lbs., the capacity of the assist crane required represents a very significant transport expense.
As a result, designers have attempted to develop self-handling systems for assembling and disassembling cranes. The majority of the self-handling systems developed thus far have been directed to smaller cranes which need to be disassembled into only a few components.
The development of self-handling systems for larger cranes, however, has met with limited success. One reason for this is that larger cranes need to be disassembled into numerous components, thus requiring time-consuming disassembly and reassembly procedures. For example, a large capacity crane typically uses a complicated and cumbersome rigging system to control the angle of the boom. Boom rigging system components such as the equalizer, the backhitch, and wire rope rigging are heavy and difficult to disassemble for transport. Another reason for the limited success of prior art self-assembling cranes is that they typically rely on additional crane components that are used only for assembling and disassembling the crane. For example, some self-assembling cranes require additional wire rope guides and sheaves on the boom butt so that a load hoist line can be used with the boom butt to lift various crane components during the assembly process. An example of one prior art method for disassembling a typical large capacity crane is disclosed in U.S. Pat. No. 5,484,069.
It is therefore desirable to provide a crane and method of self-assembly which reduces the number of parts which must be derigged and removed to disassemble the crane for transport. In addition, it is desirable to eliminate components which are only used during the crane assembly process. A crane which uses one or more hydraulic cylinders as boom hoist cylinders to control the boom angle would thus be advantageous.
Cranes and other equipment often use hydraulic actuators, primarily motors and cylinders, to power the components of the equipment. The hydraulic power for such actuators is normally supplied by one or more diesel engines powering one or more hydraulic pumps. The hydraulic systems for cranes and other equipment have ordinarily been open loop systems, where hydraulic fluid is drawn from a low pressure reservoir, such as an atmospheric pressure tank, into the intake of the pump. Fluid expended by the actuators is returned to the reservoir. Closed loop hydraulic systems are more energy efficient, but generally are more complicated. It would be advantageous if a closed loop hydraulic system would be used to operate the various components of the equipment, including the boom hoist cylinders.
Prior art hydraulic circuits are known for operating double-acting hydraulic cylinders with a closed loop pump. For example, U.S. Pat. No. 3,425,574 to Willgrubs et al. discloses a power shovel with a double-acting cylinder. Closed loop piston pumps are used to power the cylinder in both directions by changing the direction of the motor powering the pumps. The cylinder of Willgrubs has a ratio of the change of volume of the rod end of the cylinder to the change in volume of the piston end of the cylinder of about 1:2.78. The additional fluid needed to compensate for this difference in volume is taken care of by four vane pumps. However, because of the arrangement of the system, the vane pumps add fluid to the closed loop portion of the circuit by discharging into the high pressure side of the circuit.
In preferred aspects, the invention provides a crane having one or more hydraulic boom hoist cylinders and a hydraulic circuit to control the hydraulic boom hoist cylinders.
In one aspect, the invention is a crane having an upper works rotatably mounted on a lower works and a boom pivotally mounted on the upper works comprising a mast pivotally connected to the upper works; a double-acting hydraulic cylinder having a bore, a piston mounted in the bore and forming a piston end of the cylinder, and a rod connected to the piston opposite the piston end and extending out of an exit end of the bore but being sealed at the exit end of the bore, thus forming a rod end of the cylinder, the cylinder having a first passageway in communication with the piston end and a second passageway in communication with the rod end, one of the piston end of the cylinder and the rod being pivotally connected to the upper works and the other of the piston end of the cylinder and the rod being pivotally connected to the mast; a closed loop hydraulic pump having, during operation, a low pressure port in fluid communication with a low pressure side of the hydraulic circuit and a high pressure port in fluid communication with a high pressure side of the hydraulic circuit; and a directional flow controller and hydraulic lines connecting the closed loop pump and the double-acting cylinder such that fluid from the pump can be directed to either the first or second passageways and fluid from the other of the first or second passageways is then directed to return to the pump.
In a second aspect, the invention is hydraulic circuit comprising a first double-acting hydraulic cylinder having a bore, a piston mounted in the bore and forming a piston end of the cylinder, and a rod connected to the piston opposite the piston end and extending out of an exit end of the bore but being sealed at the exit end of the bore, thus forming a rod end of the cylinder, the cylinder having a first passageway in communication with the piston end and a second passageway in communication with the rod end; a closed loop hydraulic pump having, during operation, a low pressure port in fluid communication with a low pressure side of the hydraulic circuit and a high pressure port in fluid communication with a high pressure side of the hydraulic circuit, a directional flow controller and hydraulic lines connecting the closed loop pump and the double-acting cylinder such that fluid from the pump can be directed to either the first or second passageways and fluid from the other of the first or second passageways is directed to return to the pump, a second hydraulic pump in fluid communication with the closed loop hydraulic pump so as to supply make-up hydraulic fluid to the low pressure side of the hydraulic circuit when the rod is being extended; and a relief valve in fluid communication with the first passageway when the rod is being retracted to allow excess hydraulic fluid to flow out of the circuit.
In the present invention, the use of a hydraulic cylinder pivotally connected at one end to the upper works of a lift crane and at the other end to the mast, and used to control the boom angle, is a significant advantage over other commercial cranes in use today. Further, to be able to use a double-acting cylinder for the boom hoist function, and to be able to use a closed loop pump to power the cylinder, is a further unique feature of the crane. The unique hydraulic circuit of the present invention allows a double-acting hydraulic cylinder to be powered by a closed loop pump, with make-up fluid needed when the cylinder is being extended to be supplied by a second pump feeding the low pressure side of the closed loop pump.
These and other advantages, as well as the invention itself, will become apparent in the details of construction and operation as more fully described and claimed below.